1. Field of the Invention
This invention relates to improvement in the art of sealing of packages, and particularly to an improved apparatus for continuous ultrasonic sealing of packages made on a form and fill packaging machine.
2. Prior Art
Form and fill packaging machines are well known and commonly used in the prior art. In such machines a web of packaging material is directed to a forming shoe where it is formed into a tubular configuration and sealed longitudinally along its edges (back seal). The tube is also sealed transverse to its length and product is fed into the tube while it is being formed into packages. That is, the formed tube of packaging film has an end seal made transversely thereacross, the tube moves while the longitudinal or back seal is made and product inserted, then another end seal is made and the filled package is severed. This operation continues intermittently as movement of the packaging material is halted for making the end seal.
Typically, intermittent motion form and fill packaging machines use thermal transfer or thermal impulse seal equipment to provide the end seal. A typical example of known prior art form and fill machines is shown in expired U.S. Pat. No. 2,899,875 to W. C. Leasure.
The intermittent motion of intermittent form and fill machines is, obviously, a limitation of the machine's productive capabilities. If a form and fill machine could make a suitable end seal with the web moving continuously the dwell cycle could be removed and the capacity significantly increased.
The intermittent motion form and fill machines have historically had problems in seal continuity of the back seals produced thereon. It has also been difficult to provide a uniform quality multi-layer end seal with the conventional known prior art heat sealing. The use of heat transference through various package mediums as currently practiced with thermal seal systems is problem creating due to the fact that packaging material is commonly insulating and this thermal system is also energy intensive, i.e., a high user of electrical power.
It has also been known to use ultrasonics in connection with form and fill machines, that is the use of ultrasonic sealing of packages prepared on a form and fill machine. One such example is my prior patent, U.S. Pat. No. 4,373,982. This patent, however, is directed to providing a longitudinal or back seal for overlapping or fin-type edges and is directed specifically to an intermittent form and fill machine, although the concept disclosed in such patent is also capable of use in connection with a continuously moving form and fill machine.
There is a need in the art for ultrasonic sealing, not only of the longitudinal or back seals, but also the end seals so that a sealing machine can be completely ultrasonic. There is need in the art of form and fill machines for improvement of capacity by eliminating intermittent motion while providing high quality sealing without relying on adhesives and to be able to accomplish uniform high quality multi-layer gusseted end seals. There is also need in the art to eliminate the problems in connection with heat transference to various packaging films as experienced with current thermal seal systems in the form and fill machine art.